DENIERS SAY:

There's nothing new about extreme weather — ever heard of the Dust Bowl?

SCIENCE SAYS:

Climate change "loads the dice" and makes extreme weather more likely to happen.

When we pollute the atmosphere with dirty energy like oil, coal, and gas, we end up with dirty weather. Around the world, devastating extreme weather events are becoming more common and severe. Take the United States, which during 2012 alone experienced the worst drought in decades, two of the most destructive wildfires in its history, and the unprecedented devastation from Superstorm Sandy. Of course, bad weather has always been with us, but climate change greatly increases our risk of extreme weather like heavy storms, droughts, and heat waves. We are playing games with our weather system with loaded dice. And the odds are not in our favor.

Additional info from The Climate Reality Project

When it comes to the relationship between climate change and extreme weather, there's no more comprehensive a source than the major report released this spring by the United Nations Intergovernmental Panel on Climate Change (IPCC). A product of worldwide collaboration and consensus, with sign-off from nearly 200 countries, the report confirms what scientists have long been telling us: Manmade climate change has increased our vulnerability to devastating extreme weather events such as heat waves, heavy rains and drought. And the more we pollute, the worse things will get.

Climate change affects our weather, in large part, by intensifying the water cycle. In short, water evaporates into the atmosphere from the land and ocean and returns to Earth’s surface in the form of rain and snow. As the world warms, the rate of evaporation from the ocean seems to be increasing. Think about heating a large pot of water on your stove — the higher you turn the dial, the faster the water evaporates.

But that's not all. Warmer air can hold more water vapor (PDF), which can lead to more intense, supercharged rainstorms. The intensity of downpours (and therefore the risk of floods) depends in part on how much water the air can hold at a given time.

So far, it sounds like the world is getting wetter, right? But we also know that climate change also increases the risk of severe drought. How does that work? Contrary to what you might expect, more intense rain doesn’t necessarily mean wetter soils. Rain that falls as a violent downpour doesn’t do much to help crops or other plants. Instead of gently soaking into the soil, heavy rain can cause flooding, but then all that extra water quickly runs off into rivers to be carried back to the sea.

Furthermore, evaporation dries out soils and plants. Think about watering your lawn on a scorching hot afternoon. Some of the water from your sprinkler evaporates before it even hits the grass, and the rest has little chance to soak into the soil before it moves back into the air.

This graphic illustrates how global warming changes the water cycle, and in turn is changing the weather we see outside.

We’ve always had extreme weather, and we always will. But the bottom line is this: Climate change is increasing our risk of extreme weather. Just as a baseball player on steroids is more likely to hit a home run, higher temperatures, heavier rain, intensified droughts and stronger storms are more likely to occur if we pump carbon pollution into the air. Climate change, in essence, means “weather on steroids".